1. Field of the Invention
The present invention relates to a magnetoresistance effect type thin film magnetic head adapted for averting the characteristic instability in a playback mode while minimizing unsteady generation of noise.
2. Description of the Prior Art
In a conventional magnetoresistance effect type thin film magnetic head having a shielding structure, a magnetoresistance effect element (MR element) 2 is so disposed on a substrate 1 that, as illustrated in FIG. 5, its longitudinal direction becomes parallel with a head contact surface a (vertical to the drawing paper face), and electrodes (not shown) are led out from both ends of the MR element 2, while shielding magnetic layers 4 and 5 are disposed above and below the MR element 2 through an insulator layer 3. In such MR element 2, a sense current supplied thereto flows orthogonally to a signal magnetic field generated from a magnetic recording medium, and the two electrodes are exposed on the magnetic head surface a. Therefore, in such conventional thin film magnetic head 6, the electrodes at both ends thereof are brought simultaneously into contact with the main surface of a conductive magnetic recording medium formed by sputtering or the like on a disk particularly in a hard disk device. Upon contact of the two electrodes with the disk surface, an electrical resistance change occurs between the electrodes in addition to the electric resistance change in the MR element 2 and then causes generation of great noise.
For the purpose of solving the problems mentioned, there is proposed an improved thin film magnetic head 8 wherein, as illustrated in FIG. 6, an MR element 12 is disposed vertically to a head surface a, and two electrodes 7A and 7B are led out from both ends of the MR element 12. One electrode 7A at the fore end is exposed on the magnetic head surface a while the other electrode 7B at the rear end is positioned inside the magnetic head without being exposed on the magnetic head surface a, and a sense current i supplied to the MR element 12 is caused to flow in the same direction as a signal magnetic field generated from a magnetic recording medium.
In such thin film magnetic head 8, a bias conductor 9 is formed for applying a bias magnetic field to the MR element 12, and shielding magnetic layers 4 and 5 are disposed through an insulator layer 3 above and below the MR element 12 inclusive of the bias conductor 9. In this structure, the electrodes 7A and 7B are formed to be thicker than the MR element 12 and are composed of a high-conductivity metallic material, so that the electric resistance change caused between the electrodes 7A and 7B is so small as to be negligible despite contact of the fore end electrode 7A with the disk surface, thereby inducing no great noise. Further in the above proposal where the MR element 12 is composed of two magnetic layers 12b and 12c via a nonmagnetic intermediate layer 12a, it is possible to certainly avert generation of Barkhausen noise that may otherwise be derived from movement of a magnetic wall.
There are generally known two types relative to the thin film magnetic head having the MR element 12 where a sense current is caused to flow in the same direction as a signal magnetic field. One type is such as shown in FIG. 6 where the MR element 12 and one electrode 7A are exposed on the magnetic head surface a; and the other type (not shown) is such that the MR element 12 is positioned inside, and a signal magnetic field is led to the MR element 12 by way of a magnetic member termed a yoke. The former thin film magnetic head is considered to be superior with respect to the sensitivity.
The upper and lower shielding magnetic layers 4 and 5 provided for enhancing the reproducing resolution are usually composed of a metal such as permalloy. And the electrodes 7A and 7B for the MR element 12 are generally thicker than the MR element and are composed of a material having a low resistivity. Therefore, if the fore-end electrode 7A of the MR element 12 in the thin film magnetic head 8 of FIG. 6 happens to be short-circuited electrically to the shielding metallic magnetic layer 4 in the manufacturing process or during the operation of the magnetic head, such a fault induces disorder of the reproducing characteristics and generation of noise.
Since the reproducing gap l defined between the shielding magnetic layer 4 and the MR element 12 is practically as small as several thousand angstroms (0.6 to 0.3 microns), it has been unavoidable that entrance of any extremely small conductive dirt during the magnetic head operation or any incomplete insulation in the manufacturing process renders the reproducing characteristics unstable.
Meanwhile in the thin film magnetic head of FIG. 6 where the fore end of the MR element is exposed on the magnetic head surface a, there exist some problems including abrasion and erosion, but such problems have already been mostly solved. However, an undesired phenomenon may occur in that the MR element can be suddenly broken during the operation of the magnetic head or at the rise and halt thereof, to consequently fail.
As a result of studying the above mechanism, the following has been found as illustrated in FIG. 8 where a magnetic disk 14 serving as a recording medium is disposed rotatably on a spindle 15 in a hard disk device. Denoted by 8 is an MR thin film magnetic head.
When a stationary state illustrated in FIG. 8A is changed to an operating state of FIG. 8B, the surface potential of the magnetic disk 14 is increased due to the rotation of the magnetic disk 14 (see FIG. 9). The potential difference V.sub.1 -V.sub.0 may reach 20 volts or so and, if the thin film magnetic head 8 is brought into contact with the magnetic disk 14 under such condition (as in a stopping state of FIG. 8C), the static charge on the surface of the magnetic disk 14 is released therefrom to the MR element to consequently damage the same. Meanwhile, when the thin film magnetic head 8 is in contact with the magnetic disk 14 in a stationary state, the above damage can be prevented by opening the circuit of the MR element. However, during the magnetic head operation (in a flying state), the distance d between the magnetic disk 14 and the thin film magnetic head 8 is as small as 0.1 to 0.3 micron, so they may be brought into mutual contact by some dirt or vibration, and no adequate countermeasures for such a trouble have been contrived heretofore.